Re: Zotac gtx 480
Zotac is just the company that makes the cards, NVIDIA Make the GTX 480 chip.
It is important for SLI'd cards to be chips in the same series, like a GTX 460 and GTX 480 could be SLI'd, but a GTX 460 and a GTX 560 can't.
same for ATI, a 5770 could be crossfired with a 5750 but not a 5870.
but, i think, most commonly people will SLI or Crossfire two identical cards to rule out any possibility of problems, besides the normal risks associated with hardware such as static and DOAs.
if you're going to get a Zotac GTX 480 (and btw, i would recommend going with EVGA GTX 480 instead, since they are better quality from my experiences) get an identical card to SLI it with, since then there's no chance of any incompatibility.
EVGA SLI Micro Z68 // Intel i5-2500k // 8GB Corsair Vengeance 1866MHz // Overclocked 2GB MSI R9 270X // Corsair Carbide SPEC-03 // Kingston Hyper-X 120GB // 2TB WD Green + 500GB WD Black